Shaft furnace



Sept. 7, 1965 BECKENBACH SHAFT FURNACE Filed April 27. 1962 2 Sheets-Sheet 1 J in $55 Fig. lb.

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Sept. 7, 1965 K. BECKENBACH SHAFT FURNACE 2 Sheets-Sheet 2 Filed April 27. 1962 United States Patent 3,204,936 SHAFT FURNA'CE Karl Beckenbach, Hildeguudisallee 3'3, Buderich, near Dusseldorf, Meererbusch, Germany Filed Apr. 27, 1962, Ser. No. 190,729 Claims priority, application Germany, June 21, 1961, B 62,980 13 Claims. '(Cl. 263-29) The invention relatesto a shaft furnace for heat treatment of a fluent mass of solid material such as limestone, dolomite, magnesite and similar material introduced in the upper end of the furnace and descending therein through the following sections or zones a preheating section, a combustion section and a cooling section before being discharged from the lower furnace end, there being provided means for introducing cooling air at the lower part of said cooling section into the descending material to flow upward therein in heat absorbing relation therewith, means for introducing fluid fuel into the combustion section at spaced points of said section and means for escape of the combustion gases at the upper end of the furnace.

In the new shaft furnace, furnace temperatures in the lower region of the firing or combustion zone or section are intended to be kept lower than in the upper region of the said zone. This is in order to avoid over-combustion of the material being burnt, and is of importance especially in the production of soft-burnt lime. In this connection, the temperatures in the lower region of the firing or combustion zone should not exceed about l150 at any point.

In order to reduce temperatures in the lower region of the firing or combustion zone, it is known to introduce only some of the fluid fuel, i.e. liquid or gaseous fuel required for the whole combustion process into the furnace in this region, while the remainder of the fuel is introduced into the upper firing or combustion zone at one or more higher points on the furnace. When the fuel is split up in this way, if the cooling air distributed over the whole cross-section of the material column enters the lower combustion zone, the average temperature in the lower region of this zone will be relatively low because combustion of the relatively small quantity of fuel introduced in this region takes place with a large excess of air.

In order to attain gentle burning in the lower part of the combustion zone, it has furthermore been proposed to dilute the combustion gases introduced at the lower end of the combustion zone with burnt out combustion gases hereinafter referred to as exhaust gases taken at high temperatures from the furnace at the upper end of the combustion zone, and at the same time to take the major part of the cooling air from the furnace at the upper end of the cooling zone, and re-introduce it into the furnace in the upper region of the combustion zone. There is then only relatively little air available in the lower region of the combustion zone for combustion of the combustion gases diluted with hot exhaust gas introduced at the lower end of the said zone, so that it is impossible, or not completely possible, to realise the intention of the idea of the invention, namely to run with a large excess of air in the lower combustion zone.

Besides the long pipe-line required, taking the exhaust gas to be added from the upper end of the combustion zone has the following disadvantage in principle: As the exhaust gas must be taken off at fixed points in the furnace and its masonry, the temperature of the exhaust gas must not be too high because of appliances disposed in the exhaust pipe, for example blowers. However, the exhaust gas temperature must also not be below about 3,204,936 Patented Sept. 7, 1965 900 C., because recirculation of exhaust gas at low temperatures has the effect of reducing the thermal efficiency of the furnace. Since the combustion zone moves upwards when the furnace is more heavily loaded, i.e. extends into the higher part of the furnace, maximum combustion-zone temperature, i.e. a temperature of 1400 C. or more, may now therefore prevail, when the furnace is on high output, at the point where exhaust gas was previously drawn off at a temperature of 900 C. with the furnace on low output. If the exhaust gas take-off were arranged very high above the combustion zone in order to exclude excessively high exhaust gas temperature in every case, the exhaust gas temperature would be below 900 C. with the furnace on low output, with resulting poor efiiciency in the plant.

The invention adopts another way of attaining the desired low combustion temperatures in the lower region of the combustion section or zone, and at the same time preventing excessive temperatures in the whole region of the combustion zone. According to the invention, this is done by taking the exhaust gas not from the upper, but from the lower part of the combustion section or zone, with the result that the described disadvantages resulting from take-off from the upper combustion zone are avoided. Exhaust gas can be taken from the lower combustion zone at temperatures which are substantially more constant than at the upper combustion zone. Since the attainment of soft-burnt lime anyhow involves the use of all means to keep temperatures in the lower combustion zone lower than in the upper combustion zone, i.e. keeping to temperatures which are not more than 1150 C., but on the other hand must be more than 900 C., the correct exhaust gas temperature is always present here. This temperature is substantially independent of fluctuations in furnace output, the more so since the distance between the fixed exhaust gas outlet and where the fuel is introduced is always the same.

According to the invention, at least some of the exhaust gases and the air required for their combustion flow downwards in the lower region of the combustion zone with the material column falling in the furnace.

In shaft-furnaces in which the heated cooling air rising from the cooling zone is completely diverted from the material column at the upper end of the said zone to be re-introduced into the furnace at a higher level, it is advisable to admix the exhaust gas taken from the lower part of the combustion zone with the diverted cooling air, and to re-introduce the cooling air mixed with exhaust gas into the material column at higher points on the furnace-shaft, mixing with fuel being carried out.

In shaft-furnaces in which the gases in the lower part of the combustion zone move downwards in the material column, if all of the cooling air rising from the cooling zone is taken from the material column, the exhaust gas and cooling air can be mixed with one another as soon as they are taken off, and extracted together from the material column, as described below in the description. The exhaust gas and cooling air may, however, also be taken off at points arranged at a distance from one another in the vertical direction, so that a so-called stewing zone, in which gases do not flow through the material or flow through it only to a small extent, remains between the extraction points or between the combustion zone and the cooling zone.

The large excess of air used here in order to attain low soft-burning temperatures in conjunction with the admixed exhaust gas is thus constant over the whole crosssection and at all parts thereof, so that a uniform and low combustion can be maintained everywhere here. The downward flow used here furthermore has the great advantage that falling temperatures occur in just that part of the furnace in which the last fine-burning occurs.

It is advisable to burn the combustion gases in the lower part of the combustion Zone with a large excess of air. Combustion with a large excess of air ensures that the fuel introduced in the lower combustion zone is completely burnt, so that the exhaust gas taken from this zone and admixed with the diverted cooling air no longer contains any combustible components, and further more is at relatively low temperature, so that it can also be delivered by blowers.

Acceleration may be imparted to the reversed exhaust gas or mixture of exhaust gas and cooling air, or if desired only to the cooling air, by injectors operated with additional air at higher pressure, or with heating gas fed is at higher pressure in the case of a gas heated furnace, or this may also be done by fans.

According to the invention, a tubular insert arranged concentrically with respect to the axis of the furnace is provided for this purpose in the furnace shaft. The hollow space in this insert is provided with inlet apertures at the height of the lower end of the combustion zone, and with outlet apertures at the height of the fuel feed points to the upper combustion zone, and gases from the shaft enter and emerge from the hollow space respectively through the said apertures.

The shaft insert with gas-inlet apertures at the lower end of the combustion zone and gas outlet apertures at higher points on the shaft, which insert represents an essential device feature of the invention, may, however, also be used merely for diverting the cooling air, in which case the cooling air emerges into the shaft either directly at these higher points or via pipes inside ribs connecting the insert to the walls of the furnace, is fed to the fuel feed points and then passes, mixed with fuel, into thhe shaft.

In order that the invention may be well understood there will now be described a plurality of embodiments thereof, given by way of example only, reference being had to the accompanying diagrammatic drawings in which:

FIGURE 1a is a fragmentary vertical cross-sectional view showing the middle portion of a shaft furnace having a blower fan for extracting exhaust gas and cooling air in the region of the lower combustion zone of the furnace.

FIGURE lb is a fragmentary vertical cross-sectional view of a shaft furnace similar to FIGURE la but showing an injector type device for taking off and extracting exhaust gas and cooling air.

FIGURE 2 is a vertical cross-sectional view of a modified form of the invention and FIGURE 3 is a horizontal cross-sectional view taken on line 3-3 of FIGURE 2 and looking in the direction of the arrows.

For the sake of greater clarity, only the middle portion of the shaft furnace, comprising the upper and lower parts of the combustion section and the upper part of the cooling section are illustrated. The pre-heating section disposed above the upper part of the combustion section and the charging devices arranged above the same are not shown. The zonal regions of the furnace are diagrammatically indicated by means of dashed lines. The same parts are designated with the same reference numbers in FIGURES 1a to 3.

Each of the furnaces diagrammatically shown in the figures comprises in its wall 10 two galleries of fuel-feed points uniformly distributed over the periphery of the furnace, only three being illustrated or indicated in each case in the elevations shown. The fuel-feed points in the upper gallery arranged in the upper part of the combustion zone are designated by 12, and those in the lower gallery arranged in the lower part of the combustion zone by 14. The number of fuel-feed points, at each of which there may be one or more burners, may also be greater or less than four. The fuel-feed points in one gallery may either be at the same height or be graduated in height,

the latter more particularly when there are ribs extending transversely through the furnace shaft in the vicinity of the fuel-feed points in order to attain more uniform distribution of furnace gases over the cross-section of the furnace. Furthermore, there is a precombustion chamber at each of the feed points. The precombustion chambers for the lower feed points are designated by 1511, and those for the upper ones by .1512. Furthermore, different forms of devices for accelerating exhaust gas or air taken from the furnace, which device takes the form of fans in the case of the arrangement shown on the left hand side of these figures, and injectors in the case of the arrangement shown in the right hand side.

As illustrated in the drawing, there are throttle valves or the like in the pipe system, in order to regulate the composition of the exhaust gas-air mixture flowing in from the fan or injector, or to regulate the distribution of the accelerated mixture to the fuel feed points in the upper and lower combustion zones.

In the form of embodiment illustrated in FIGURES 1a and lb there is a central insert 59a in the middle of the shaft, which extends as far as the base (not illustrated) of the furnace, and is supported there. Gas accelerating devices 30 and 32 are used with this arrangement also. The exhaust gas-air mixture rising in the cylindrical space 53 is fed through apertures 55 and pipes 57 arranged in roof-shaped ribs 56 to an annular collector pipe 58, whence it is aspirated via a pipe 59 by the fan 30 or the injector 32., The gas passes from the pressure side of the device 30, 32 to the fuel feed points 12, 14-. In this case also, some of the gases emerging from the pre-combustion chambers 15a flow upwards, and some downwards in the direction of material movement, and having flowed downwards they enter the cylindrical space 53 through the apertures 60 at the upper end of the cooling zone, together with the cooling air. Radial roof ribs may be arranged above the pre-combustion chambers with this embodiment.

FIGURES 2-3 show a further form of embodiment of a shaft furnace working in accordance with the process of the invention, and comprising a tubular middle portion to the furnace in a similar manner to the form of embodimcnt shown in FIGURES la-1b. The middle portion of the furnace takes the form of a cylindrical insert 61, which is suspended from girders 62 fastened in the upper end of the furnace, and consists of a double-walled steel cylinder 63 with a fireproof lining 65 over its whole length externally and also towards the bottom internally. The steel cylinder is provided, in those portions having a fireproof sheathing, with projecting sheet-metal ribs to support the radial bricks of the lining. These sheet-metal ribs are not illustrated. The annular duct 66 disposed between the two walls of the steel cylinder 63 serves to guide cooling air, as described below in detail.

The hollow space 67, open at the bottom, in the lower part of the insert is closed at the top, approximately at the height of the lower end of the upper combustion zone, by a partition 68 made of fireproof material.

The shaft insert 61 is attached to the furnace wall 59 by a number of radially extending angular ribs, hereinafter also called roof ribs on account of their roof-like design. In the example of embodiment shown, there are two rows or stories of roof ribs at a distance from one another in the region of the combustion zone of the furnace, the upper ones being designated by 70, and the lower ones by 71. The ridge-line of the roof ribs 71 is designated by 71a in FIGURE 3.

The upper and lower roof ribs 70 and 71, whereof there are five each in the example of embodiment shown, are

/ in the same plane, but may also be offset in height if However, for the sake of simpler illustration both stories are shown mutually superposed.

Each of the ribs 70 and 71 comprises two passages.

The upper of these passages 72 are connected at their inner ends to the annular duct 66. Their outer ends pass through the furnace wall and are open, so that ambient air can pass into the annular duct 66, and can be led into the open, from the upper end of the shaft insert, through a boxed in girder and a chimney-like tube 94 fastened thereto. The lower passages 75 are in communication at their inner ends with the hollow space 67. Their outer ends are disposed inside extensions 76 projecting from the furnace wall. In these extensions 76 there are pre-combustion chambers 77 with a highly fire-proof lining beneath the passages 75, and the inner ends of the said chambers open out into the hollow spaces in the material filling which are present beneath the roof ribs. There are burners 78 at the outer ends of the pre-combustion chambers.

The lower passages 75 are bent up near their outer ends. To these bent-up ends are connected connector tubes 79 extending obliquely downwards in the direction of an extension 76 adjacent to the said ends, the said tubes being designated after the manner of injectors. These tubes 79 designated after the manner of injectors open out tangentially at 80 into the pre-cornbustion chambers of the adjacent extension. The driving air feed tube 81 projecting into the injector tube 79 is connected to an annular pipe 82 to which the primary air pipes 83 for the burners 76 are also connected. The pipes 81 and 83 are provided with regulator members which are not illustrated.

The annular pipe 82 is connected to the outlet tube 84, emerging from the upper end of the furnace, of a recuperator 85 suspended from the girders 62 into the upper end of the insert 61. The recuperator 85 consists of a substantially cylindrical hollow member 86, subdivided into a small upper exhaust gas chamber 87 and a large lower air chamber 88. Some of the exhaust gas leaving the combustion zone flows into the insert through apertures 89 in the Walls thereof, and then through tubes 90 passing through the air chamber 88 into the exhaust-gas chamber 87 of the recuperator, from which it is fed via a pipe 91 to the suction union of an exhaust gas fan 92, whence the exhaust gas flowing to the upper end of the furnace through the material is aspirated via a tube 93. The proportion of exhaust gas flowing through the recuperator may be regulated by setting regulator members 94a and 94b.

The upper end of the air chamber 88 of the recuperator is connected via a pipe 95 extending through the exhaust gas chamber to the pressure side of a fresh-air fan not illustrated. The hot air outlet tube 84 passes through this pipe 95, and extends as far as the vicinity of the lower end of the air chamber 88.

The air rising in the cooling zone may be forced into the lower end of the furnace by a fresh-air fan not shown.

The new furnace arrangement may be operated in various ways. For example, if the furnace is to serve for producing a soft-burnt lime, it is desirable on the one hand, in order to attain a high degree of heat economy, for the limestone to be so intensively de-acidified at high combustion-gas temperatures in the upper region of the combustion zone, but with the smallest possible excess of air, that the de-acidification process has already made a large amount of progress when the limestone reaches the lower region of the combustion zone. On the other hand, a temperature of about 1150 C. should if possible not be exceeded during the remainder of de-acidification in the lower region of the combustion zone. Both conditions are complied with in the new furnace arrangement, for example if the smaller proportion of the fuel in the region of the lower combustion zone is fed via the lower story of burners or combustion spaces 77 arranged approximately in the middle of the said zone, and is burnt there with a large excess of air, the speed of the air aspirated through the passages 75 in the lower roof ribs 71 from the hollow space 67 being so set by suitable regulation of the driving air feed that some of the exhaust gases emerging from the combustion spaces 77 into the hollow spaces under the roof ribs 71 flow downwards in a steady flow with the material. This downwardly flowing part of the exhaust gases is completely burnt upon reaching the lower end of the shaft insert 61. The exhaust gas temperature is also relatively low because of the large excess of air, so that the temperature of the limestone in that region of the shaft through which these gases flow can be kept to the desired level (about 1150 C.) and below. The exhaust gases still containing a large amount of excess air mix at the lower end of the shaft insert with the cooling air rising from the cooling zone of the furnace without increasing the temperature of the said air to an inadmissibly high value. I

The major part of the fuel is burnt with a small excess of air, or even starved of air, in the pre-combustion chambers disposed in the upper story of burners 78 and pre-combustion chambers 77 situated substantially at the lower end of the upper combustion zone, and all the air available for combustion purposes in that part of the furnace immediately above the roof ribs 70 is made up of the air component of the already strongly heated exhaust gas-air mixture aspirated via the passages 75 in the upper roof ribs 70, the driving air pre-heated in the recuperator, the air component of that part of the exhaust gases flowing directly upwards from the roof ribs 71 and the primary air coming from the recuperator for atomisation and pre-combustion of the fuel.

What I claim is:

1. In a shaft furnace for heat treating a fluent mass of solid material such as limestone, dolomite, magnesite and similar materials introduced in the upper end of the furnace shaft and descending through preheating, combustion and cooling zones before being discharged from the lower end of the furnace, said shaft furnace including a cylindrical wall, means for introducing air at the lower portion of said cylindrical wall and the lower portion of said cooling zone into the descending material to flow upward therein in heat absorbing relation therewith, circumferentially spaced combustion chambers disposed in said cylindrical wall located at upper and lower levels in communication with said combustion zone located at vertically spaced points of said combustion zone, burner means located in each of said combustion chambers for burning fluid fuel in said chambers, vertical tubular conduit means comprising a tubular member concentrically arranged in said shaft through which cooling air and exhaust gases of combustion are withdrawn from said shaft furnace, second conduit means having one end connected with said vertical tubular conduit at a point intermediate said cooling zone and the points of communication of said upper combustion chambers, a gas accelerating means having suction and pressure sides, the other end of said second conduit means being connected with the suction side of said gas accelerating means, and duct means connecting the pressure side of said gas accelerating means to said combustion chambers, whereby a mixture of air and combustion gases will be supplied directly to the combustion chambers of said burner means in the immediate vicinity of the flame from said burning fluid fuel, and means to permit the escape of excess exhaust gases at the upper open end of said cylindrical wall shaft furnace.

2. In a shaft furnace for heat treating a fluent mass of solid material such'as limestone, dolomite, magnesite and similar materials introduced in the upper end of the furnace shaft and descending through preheating, combustion and cooling zones before being discharged from the lower end of the furnace, said furnace comprising means for introducing air at the lower portion of said cooling zone into the descending material to flow upward therein 'in heat absorbing relation therewith, upper and lower combustion spaces disposed in the shaft wall communicating with said combustion zone at vertically spaced points of said combustion zone, burner means in each of said combustion spaces for burning fluid fuel in said spaces, conduit means through which cooling air and exhaust gases are withdrawn from said shaft, said conduit means comprising a hollow vertically extending member within said shaft furnace, said conduit means being in communication adjacent one end with said shaft in the area of said cooling zone and said points of communication of said lower combustion spaces, gas accelerating means having suction and pressure sides, first duct means connecting said conduit means to the suction side of said gas accelerating means with the pressure side of said gas accelerating means connected by second duct means directly to said combustion chambers in close proximity to the flame of said burning fluid fuel, and means to permit the escape of exhaust gases at the upper portion of said shaft furnace.

3. In a shaft furnace according to claim 2, character ized in that at least a blower is used as gas accelerating means.

4. In a shaft furnace according to claim 2, characterized in that at least an injector is used as an air accelerating means.

5. In a shaft furnace for heat treating a fluent mass of solid material such as limestone, dolomite, magnesite and similar materials introduced in the upper end of the furnace shaft and descending through preheating, combustion and cooling zones before being discharged from the lower end of the furnace, said furnace comprising a shaft wall, means for introducing cooling air at the lower portion of said cooling zone into the descending material to flow upward therein in heat absorbing relation therewith, combustion chambers at upper and lower levels disposed adjacent said shaft Wall communicating with said combustion zone at vertically spaced points of said Zone, burner means in each of said combustion spaces for burning fluid fuel in said spaces, first conduit means through which cooling air is withdrawn from said shaft, said first conduit means comprising a vertical tubular member arranged in said shaft in communication at one end with said shaft at the upper end of said cooling zone, second conduit means connected to said first conduit means through which exhaust gases are withdrawn from said shaft, gas accelerating means having suction and pressure sides, said second conduit means being connected at one end with said first conduit means intermediate said points of communication of said upper and lower levels of the combustion spaces, the other end of said second conduit means being connected with the suction side of said gas accelerating means, additional duct means connected to the pressure side of said gas accelerating means and to said combustion spaces, and means to permit the escape of exhaust gases at the upper portion of said furnace.

6. In a shaft furnace according to claim 5, characterized in that at least a blower is used as gas accelerating means.

7. In a shaft furnace for heat treating a fluent mass of solid material such as limestone, dolomite, magnesite and similar materials introduced in the upper end of the furnace shaft and descending through preheating, combustion and cooling zones before being discharged from the lower end of the furnace, said furnace comprising means for introducing cooling air at the lower portion of said cooling zone into the descending material to flow upward therein in heat absorbing relation therewith, upper and lower combustion spaces disposed adjacent the shaft wall communicating with said combustion zone at vertically spaced points of said combustion zone, burner means in each of said combustion spaces for burning fluid fuel in said spaces, conduit means comprising a central vertical tubular member in spaced relation from said shaft through which cooling air and exhaust gases are withdrawn from said shaft at the upper end of said cooling zone, said vertical tubular member extending at least through the lower combustion zone and being connected to the furnace wall by radially extending ribs disposed intermediate the points of communication of said upper and lower combustion spaces, said tubular member being provided in its wall with at least one gas inlet opening disposed at the upper end of said cooling zone and with gas outlet apertures communicating with passages extending through said ribs, gas accelerating means having pressure and suction sides, the passages extending through said ribs being connected to the suction side of said gas accelerating means, individually regulatable duct means connecting the pressure side of said gas accelerating means to :said combustion spaces, and means to permit the escape of exhaust gases from, the upper end of said shaft furnace.

8. In a shaft furnace according to claim 7, characterized in that at least a blower is used as gas accelerating means.

9. In a shaft furnace according to claim 7, characterized in that the tubular member is supported at the lower end of the furnace.

10. In a shaft furnace for heat treating a fluent mass of solid material such as limestone, dolomite, magnesite and similar materials introduced in the upper end of the furnace shaft and descending through preheating, combustion and cooling zones before being discharged from the lower end of the furnace, said furnace comprising means for introducing cooling air at the lower portion of said cooling zone into the descending material to flow upward therein in heat absorbing relation therewith, upper and lower combustion spaces disposed adjacent the shaft wall communicating with said combustion zone at vertically spaced points of said combustion zone, burner means in each of said combustion spaces for burning fluid fuel in said spaces, conduit means through which cooling air and exhaust gases are withdrawn from said shaft at the upper end of said cooling zone, said conduit means comprising a hollow space within a vertical tubular member being disposed centrally in the furnace, extending at least through the lower combustion zone and being connected to the furnace Wall by substantially radially extending ribs disposed immediately above said points of communication of said upper and lower combustion spaces, the lower open end of said member being disposed at the upper end of said cooling zone and forming an inlet opening for the withdrawn gases, said hollow space being provided in its wall with gas outlet apertures with passages extending through said ribs, gas accelerating means having pressure and suction sides, the suction side of said gas accelerating means being connected with the passages extending through said ribs, additional duct means connecting the pressure side of said gas accelerating means directly to said combustion spaces, and means to permit the escape of exhaust gases at the upper part of said furnace.

11. In a shaft furnace according to claim 10, characterized in that injectors are used for said gas accelerating means.

12. In a shaft furnace according to claim 10, characterized in that the tubular member is an insert suspended from girders arranged in the upper end of the furnace.

13. In a shaft furnace for heat treating a fluent mass of solid material such as limestone, dolomite, magnesite and similar materials introduced in the upper end of the furnace shaft and descending through preheating, combustion and cooling zones before being discharged from the lower end of the furnace, said furnace comprising means for introducing cooling air at the lower portion of said cooling zone into the descending material to flow upward therein in heat absorbing relation therewith, upper and lower combustion spaces disposed adjacent the shaft wall communicating with said combustion zone at vertically spaced points of said combustion zone, burner means in each of said combustion spaces for burning fluid fuel in said spaces, vertically extending tubular conduit means in said shaft through which cooling air and exhaust gases are withdrawn from said shaft, second conduit means connected at one end with said shaft and at the other end to said first mentioned conduit means adjacent the upper end of said cooling zone, gas accelerating means having pressure and suction sides, the first one end of said last named conduit means being connected to the suction side of said gas accelerating means, duct means for connecting the pressure side of said gas accelerating means directly to said combustion spaces in close proximity to said burner means, and means to permit the escape of exhaust gases at the upper end of said furnace, said first mentioned conduit means including a central tubular member arranged concentrically in said shaft furnace With its lower end in communication with the interior of said shaft at a point below said lower combustion spaces.

References Cited by the Examiner UNITED STATES PATENTS 2,742,276 4/53 Azbe 263--29 2,884,237 4/59 Storm et a1 26329 3,033,545 5/62 Azbe 263-29 3,142,480 7/64 Azbe 263-29 FOREIGN PATENTS 870,649 2/59 Great Britain.

0 WILLIAM F. ODEA, Acting Primary Examiner.

PERCY L. PATRICK, CHARLES SUKALO, Examiners. 

1. IN A SHAFT FURNACE FOR HEAT TREATING A FLUENT MASS OF SOLID MATEWRIAL SUCH AS LIMESTONE, DOLOMITE, MAGNESITE AND SIMILAR MATERIALS INTRODUCED IN THE UPPER END OF THE FURNACE SHAFT AND DESCENDING THROUGH PREHEATING, COMBUSTION AND COOLING ZONES BEFORE BEING DISCHARGED FROM THE LOWER END OF THE FURNACE, SAID SHAFT FURNACE INCLUDING A CYLINDRICAL WALL, MEANS FOR INTRODUCING AIR AT THE LOWER PORTION OF SAID CYLINDRICAL WALL AND THE LOWER PORTION OF SAID COOLING ZONE INTO THE DESCENDING MATERIAL TO FLOW UPWARD THEREIN IN HEAT ABSORBING RELATION THEREWITH, CIRCUMFERENTIALLY SPACED COMBUSTION CHAMBERS DISPOSED IN SAID CYLINDRICAL WALL LOCATED AT UPPER AND LOWER LEVELS IN COMMUNICATION WITH SAID COMBUSTION ZONE LOCATED AT VERTICALLY SPACED POINTS OF SAID COMBUSTION ZONE, BURNER MEANS LOCATED IN EACH OF SAID COMBUSTION CHAMBERS FOR BURNING FLUID FUEL IN SAID CHAMBERS, VERTICAL TUBULAR CONDUIT MEANS COMPRISING A TUBULAR MEMBER CONCENTRICALLY ARRANGED IN SAID SHAFT THROUGH WHICH COOLING AIR AND EXHAUST GASES OF COMBUSTION ARE WITHDRAWN FROM SID SHAFT FURNACE, SECOND CONDUIT MEANS HAVING ONE END CONNECTED WITH SAID VERTICAL TUBULAR CONDUIT AT A POINT ITNERMEDIATE SAID COOLING ZONE AND THE POINTS OF COMMUNICATION OF SAID UPPER COMBUSTION CHAMBERS, A GAS ACCELERATING MEANS HAVING SUCTION AND PRESSURE SIDES, THE OTHER END OF SAID SECOND CONDUIT MEANS BEING CONNECTED WITH THE SUCTION SIDE OF SAID GAS ACCELERATING MEANS, AND DUCT MEANS CONNECTING THE PRESSURE SIDE OF SAID GAS ACCELERATING MEANS TO SID COMBUSTION CHAMBERS, WHEREBY A MIXTURE OF AIR AND COMBUSTION GASES WILL BE SUPPLIED DIRECTLY TO THE COMBUSTION CHAMBERS OF SAID BURNER MEANS IN THE IMMEDIATE VICINITY OF THE FLAME FROM SAID BURNING FLUID FUEL, AND MEANS TO PERMIT THE ESCAPE OF EXCESS EXHAUST GASES AT THE UPPER OPEN END OF SAID CYLINDRICAL WALL SHAFT FURNACE. 